Apparatus and method for controlling reciprocating compressor

ABSTRACT

Disclosed is an apparatus and method for controlling a reciprocating compressor capable of inexpensively and exactly controlling a position of a piston in a cylinder, by which a top clearance is minimized according to the information of a phase difference between a square wave of a piston stroke and a square wave of a current supplied to the compressor. The apparatus comprises a driving section for driving the reciprocating compressor by varying an angle or ignition in response to a control signal; a current phase detecting section for outputting a square wave corresponding to the detected current supplied to the compressor; a stroke phase detecting section for outputting a square wave corresponding to a stroke of the compressor; and a control section for controlling the angle of ignition of the driving section according to the phase difference between the square wave produced from the current phase detecting section and the square wave produced from the stroke phase detecting section.

TECHNICAL FIELD

[0001] The present invention relates to a reciprocating compressor, andmore particularly to an apparatus and method for controlling areciprocating compressor by controlling an output voltage according to aphase difference between a piston stroke waveform and a current waveformof the reciprocating compressor.

BACKGROUND ART

[0002] Recently, a reciprocating compressor has been developed tocompress a refrigerant gas in a refrigerator and so on.

[0003] U.S. Pat. No. 5,342,176 discloses a reciprocating compressorusing a linear motion motor and a method for controlling a piston strokeof the reciprocating compressor.

[0004]FIG. 1 is a cross sectional view illustrating the construction ofa reciprocating compressor disclosed in U.S. Pat. No. 5,342,176, andFIG. 2 is a block diagram illustrating a compressor controllingapparatus for controlling a piston stroke of the refrigerant shown inFIG. 1.

[0005] According to the conventional reciprocating compressor, as shownin FIG. 1, a piston 1 reciprocates in a cylinder 2 in response to forceson magnets 4 to which the piston is connected by a yoke 3. The forces onthe magnets are caused by magnetic fields set up by current in a winding5. Piston motion is transmitted by the yoke linking the piston 1 to aspring 6, which has a spring constant K. During downward piston motion,gas or vapor at suction pressure, which is the pressure in a surroundingspace 9 and also in the lower part of a compressor interior space 10, isdrawn into the cylinder through a check valve 7. During upward motion ofthe piston, gas or vapor is initially compressed until the pressure inthe cylinder exceeds the discharge pressure, that is, the pressure in adischarge pipe 11, at which a point check valve 8 opens and gas or vaporis pushed into the discharge pipe by continuing upward motion of thepiston.

[0006] A conventional apparatus for controlling the reciprocatingcompressor as described above will now be described.

[0007] The reciprocating compressor comprises, as shown in FIG. 2, avoltage detecting section 13, connected to input terminals of winding 5,for detecting the voltage applied to the winding as a function of time,a current detecting section 12, connected to the winding 5, fordetecting the current through the winding as a function of time, acomputing section 14 for calculating a velocity of the piston using thevoltage and current values detected by the voltage and current detectingsections 13 and 12 and operating the piston stroke from the velocity ofthe piston, and a commending section 15 for comparing the stroke valueoperated at the computing section 14 and a predetermined voltage value,determining a target output voltage to compensate the difference betweenthe stroke value and the predetermined voltage value, and commanding itto a driving section 16.

[0008] A conventional method for controlling the prior reciprocatingcompressor will now be described.

[0009] Predetermined end displacement values (top and bottom deadpoints) are inputted.

[0010] By supplying a power to the motor of the compressor at a certainvalue, the voltage and current supplied to the winding of the compressorare detected as a function of time, respectively.

[0011] A displacement value of the piston is measured using the detectedvoltage and current.

[0012] By comparing the measured displacement value with thepredetermined displacement value, an error signal corresponding to thecomparison is outputted.

[0013] The voltage to be supplied to the winding of the motor is variedin corresponding to the error signal to minimize the error signal.

[0014] The step for outputting the error signal will be described.

v=(1/α)(V−L(dI/dt)−IR)   [Equation 1]

[0015] wherein, a is a transfer constant, V is the voltage applied tothe winding, I is the current detected from the winding, R is a windingresistance, L is a winding inductance, and t is time.

[0016] The velocity v of the reciprocating piston is calculated as afunction of time from the detected voltage and current in accordancewith the equation 1. The computed velocity is integrated as a functionof time to compute the alternating component of displacement of thepiston as a function of time. The computed velocity is differenced as afunction of time to compute the acceleration of the piston as a functionof time.

[0017] The alternating component of displacement is detected when thecomputed velocity is zero. Simultaneously, during a suction phase(moving towards the bottom dead point), the alternating component ofdisplacement, the acceleration and the current are detected. Thedisplacement of the reciprocating piston is calculated at the end of itsexcursion in accordance with a following equation 2.

Xc=x _(i) −x _(o)+(αa/K)I _(o)−(M/K)A _(o)   [Equation 2]

[0018] wherein, Xc is the end displacement, x_(i) is the alternatingdisplacement when the velocity is zero, x_(o) is the simultaneouslydetected alternating displacement, A_(o) is the simultaneously detectedacceleration, Io is the simultaneously detected current, M is the massof the reciprocating body, and K is the spring constant of the spring.

[0019] By comparing the command signal with the computed enddisplacement signal Xc, an error signal is generated.

[0020] The prior apparatus and method for controlling the reciprocatingcompressor using the above displacement-voltage feedback has followingdisadvantages.

[0021] Firstly, because the critical value of the dead point of thedisplacement of the piston has to be exactly calculated, the complicatedcalculation of the dead point of the displacement causes to an error.Specifically, it is necessary to carry out the complicated calculationsuch as equations 1 and 2, thereby producing an error of thecalculation.

[0022] Secondly, since expensive apparatuses such as a computer are usedto carry out the complicated calculation, the cost increases.

[0023] Finally, according to the U.S. patent, after the ideal dead pointof the displacement to be controlled is predetermined, the voltage iscontrolled in such a way that it is approached to the predetermineddisplacement. If the compressor is continuously used, the compressor iscontrolled using the predetermined displacement, in spite of thevariation of the ideal displacement due to the mechanical wear.Therefore, it is impossible to exactly control the compressor.

[0024] Japanese Patent Laid-Open Publication hei 9-112438 discloses anapparatus and method for controlling the reciprocating compressor, inwhich an operating frequency is adjusted according to a resonancefrequency so that the efficiency thereof is not reduced regardless ofthat a resonance frequency may be changed by the change of a springconstant of gas due to the fluctuation of the load.

[0025]FIG. 3 is a block diagram of one conventional control apparatusfor the reciprocating compressor disclosed in the Japanese PatentLaid-Open Publication hei 9-112438, and FIG. 4 is a block diagram ofanother conventional control apparatus for a reciprocating compressordisclosed in the Japanese Patent Laid-Open Publication hei 9-112438.

[0026] The conventional control apparatus for a reciprocating compressorshown in FIG. 3 comprises an alternating power supply section 21 forsupplying a driving power to the compressor 27 and having a controllablefrequency of the output voltage, a voltage detecting section 22 fordetecting an output voltage outputted from the alternating power supplysection 21 to the compressor 27, a current detecting section 23 fordetecting a current flowing>from the alternating power supply section 21to the compressor 27, a phase detecting section 24 for detecting a phasedifference between the output voltage detected from the voltagedetecting section 22 and the current detected from the current detectingsection 23, and a control section 25 for compensating a frequency of theoutput voltage of the alternating power supply section 21 correspondingto the phase difference detected from the phase detecting section 24 andcoinciding the frequency with a resonance frequency of a piston of thecompressor.

[0027] The conventional control method of the reciprocating compressorwill now be described.

[0028] If the driving power is supplied to the reciprocating compressor27 from the alternating power supply section 21, the reciprocatingcompressor 27 is driven. At that time, the voltage detecting section 22and the current detecting section 23 detect the current and voltageapplied to the compressor, respectively.

[0029] The phase detecting section 24 calculates a timing based on awaveform phase of the detected voltage value V and current value I, andcalculates the phase difference Dp of the current I to the voltage Vbased on the calculated results.

[0030] The control section 25 calculates a frequency compensating amountΔF corresponding to the phase difference Dp, and outputs a frequencycontrol signal to the alternating power supply section 21 correspondingto a frequency control amount Ff (Ff=Ff+ΔF).

[0031] Even if the resonance frequency Fc of the piston is fluctuateddue to the fluctuation of the load, the frequency F of the outputvoltage V of the alternating power supply section is controlled to becoincided to the resonance frequency Fc.

[0032] In addition, the control apparatus for a reciprocating compressorshown in FIG. 4 comprises an alternating power supply section 21 forsupplying a driving power to the compressor 27 and having a controllablefrequency of the output voltage, a voltage detecting section 22 fordetecting an output voltage outputted from the alternating power supplysection 21 to the compressor 27, a current detecting section 23 fordetecting a current flowing from the alternating power supply section 21to the compressor 27, a velocity detecting section 26 for detecting apiston velocity of the compressor 27 according to the detected resultsof the voltage detecting section 22 and the current detecting section23, and a frequency control section 28 for detecting a phase differencebetween the current detected from the current detecting section 23 andthe velocity detected from the velocity detecting section 26 tocompensate the frequency of the output voltage of the alternating powersupply section 21 corresponding to the detected phase difference, andcoinciding the frequency with a resonance frequency of a piston of thecompressor. The alternating power supply section 21 includes a DC powersupply section 21 a for supplying a DC power, and an inverter 21 b foradjusting the frequency of the voltage outputted from the DC powersupply section 21 a according to the control signal of the frequencycontrol section 28.

[0033] The conventional control method of the reciprocating compressorwill now be described.

[0034] The phase difference Dpie of the current I flowing from thealternating power supply section 21 to the compressor and the phasedifference Dpve of the velocity of the piston to the voltage V are to becoincided with the resonance frequency Fc, thereby becoming zero degree.Also, if the driving frequency F is higher than the resonance frequencyFc, the phase of the current I goes ahead of that of the velocity v. Ifthe driving frequency F is lower than the resonance frequency Fc, thephase of the current I is behind that of the velocity v. Accordingly,the compressor is controlled using the resonance frequency Fc variabledepending upon the load, so that if the phase of the current I goesahead of that of the velocity v. the driving frequency F is lowered,while if the phase of the current I goes ahead of that of the velocityv, the driving frequency F is raised.

[0035] However, the prior apparatus and method for controlling thereciprocating compressor disclosed in the Japanese Patent Laid-OpenPublication has following disadvantage.

[0036] In order to control the frequency of the power supplied to thecompressor, an expensive apparatus (inverter) has to be provided.Accordingly, since the cost of components is increased, it is impossibleto provide an inexpensive control apparatus.

DISCLOSURE OF THE INVENTION

[0037] Therefore, an object of the present invention is to solve theproblems involved in the prior art and to provide an apparatus andmethod for controlling a reciprocating compressor capable ofinexpensively and exactly controlling a piston stroke of a compressor.

[0038] In order to accomplish the above object, the present invention ischaracterized by controlling an output voltage to be applied to thecompressor according to a phase difference between a piston strokewaveform and a current waveform supplied to the compressor.

[0039] With the present invention, a top clearance of the piston strokeof the reciprocating compressor is determined depending upon the phasedifference between the stroke and the current. It was found by aresearch in that the top clearance becomes zero when the phasedifference is minimied.

[0040] In addition, the phase difference between the stroke and thecurrent can be exactly detected by only a pattern of the strokevariation and a pattern of the current variation. The need of detectingthe stroke variation only is unnecessary to an exact device.

[0041] The research can provide an apparatus for controlling thereciprocating compressor capable of inexpensively and exactlycontrolling the piston stroke. Specifically, the phase differencebetween a phase of the current supplied to a motor of the compressor anda phase of the stroke is set to a fluctuation point, and an inputvoltage when having the set phase difference is determined as a targetoutput voltage.

[0042] In one aspect of the present invention, there is provided anapparatus for controlling a reciprocating compressor comprising: adriving section for driving the reciprocating compressor by varying anangle of ignition in response to a control signal; a current phasedetecting section for outputting a square wave corresponding to thedetected current supplied to the compressor; a stroke phase detectingsection for outputting a square wave corresponding to a stroke of thecompressor; and a control section for controlling the angle of ignitionof the driving section according to the phase difference between thesquare wave produced from the current phase detecting section and thesquare wave produced from the stroke phase detecting section.

[0043] The current phase detecting section includes a current detectingsection for detecting the current supplied to the compressor to output adetected current value, and a first square wave generating section foroutputting a first square wave corresponding to the current detectedfrom the current detecting section.

[0044] The current phase detecting section further includes anintegrating section for integrating the current detected from thecurrent detecting section to output the integrated current to the firstsquare wave generating section.

[0045] The stroke phase detecting section includes a voltage detectingsection for detecting a voltage supplied to the compressor, a strokecomputing section for computing the stroke based on the voltage detectedfrom the voltage detecting section and the current detected from thecurrent detecting section, and a second square wave generating sectionfor generating a second square wave corresponding to the stroke computedfrom the stroke computing section to output the second square wave tothe control section.

[0046] The control section includes a phase difference measuring sectionfor measuring a phase difference between a current waveform outputtedfrom the current phase detecting section and a stroke waveform outputtedfrom the stroke phase detecting section, and an output voltagecommanding section for determining a target output voltage according toa size of the phase difference measured from the phase differencemeasuring section.

[0047] The output voltage commanding section includes a phase differencestoring section for storing the phase difference detected from the phasedifference measuring section, a phase difference comparing section forcomparing the phase difference stored in the phase difference storingsection with the phase difference measured from the phase differencemeasuring section, and a determining section for determining the voltageto be supplied to the compressor according to the compared result fromthe phase difference comparing section and outputting a write enablesignal of the phase difference storing section.

[0048] The determining section determines whether a top of clearance iszero when the phase difference is minimized.

[0049] The determining section outputs a write enable signal so thatwhen the phase difference detected from the phase difference measuringsection is lower than that stored in the phase difference storingsection, the phase difference storing section stores the phasedifference detected from the phase difference measuring section.

[0050] The driving section includes a TRIAC for supplying the power tothe compressor in response to a control signal, and a phase controlsection for controlling an angle of ignition for controlling the strokeof the compressor according to a control signal outputted from thecontrol section and outputting the signal to the TRIAC.

[0051] The TRIAC switches the power according to the angle of ignitionoutputted from the phase control section.

[0052] The apparatus further comprises a zero crossing detecting sectionfor detecting a zero crossing of a voltage of the power supplied fromthe driving section.

[0053] In another aspect of the present invention, there is provided amethod for controlling a reciprocating compressor, the method comprisingthe steps of: a) driving the compressor by varying an angle of ignition,and measuring a phase difference between a current phase supplied to thecompressor and a stroke phase of the compressor when the angle ofignition is varied; and b) comparing the measured phase differences, anddriving the compressor at the angle of ignition corresponding to aninflection point of the phase difference.

[0054] The phase difference is minimized at the inflection point.

[0055] The current phase is generated by detecting the current suppliedto the compressor and integrating the detected current.

[0056] The stroke phase is outputted as a pulse corresponding to anestimated value after detecting the voltage and the current supplied tothe compressor and estimating the stroke using the detected voltage andcurrent.

[0057] The step a comprises the steps of storing the detected phasedifference when driving the compressor at an initial angle of ignition;measuring the phase difference by varying the angle of ignition in adesired direction, comparing the measured phase difference with apreviously stored phase difference; substituting the measured phasedifference for the stored phase difference if the measured phasedifference is smaller than the stored phase difference; and repeatingthe measuring, comparing and substituting steps by varying the angle ofignition in same direction.

[0058] The method further comprises the step of varying the angle ofignition in a direction opposed to the previously varied direction, ifthe measured phase difference is larger than the initially stored phasedifference.

[0059] The compressor is controlled by recognizing the angle of ignitionas an inflection point of a previous step, if the measured phasedifference is larger than the previously stored phase difference.

[0060] At the step a, the phase difference is measured by setting theangle of ignition to supply the current of sufficiently small value tothe compressor at early stage and by varying the angle of ignition tosupply the current of gradually increasing value to the compressor, andat the step b, the compressor is controlled by recognizing the angle ofignition as the inflection point of a previous step, when the measuredphase difference is larger than the previously stored phase difference.

[0061] In still another aspect of the present invention, there isprovided a method for controlling a reciprocating compressor, the methodcomprising the steps of: a) measuring and storing a phase differencebetween a first square wave corresponding to a current supplied to thecompressor and a second square wave corresponding to an estimated strokeof the compressor, by driving the compressor at a desired angle ofignition; b) measuring a phase difference between a first square wavecorresponding to the current supplied to the compressor and a secondsquare wave corresponding to an estimated stroke of the compressor, bydriving the compressor at varied angle of ignition in a desireddirection; c) comparing the measured phase difference with a storedphase difference, to vary the angle of ignition in an opposed direction,if the measured phase difference is larger than the stored phasedifference, and to substitute the measured phase difference for thestored phase difference and vary the angle of ignition in samedirection, if the measured phase difference is smaller than the storedphase difference; and d) repeating the steps b and c to drive thecompressor at a point in which the phase difference is deflected.

[0062] In still another aspect of the present invention there isprovided a method for controlling a reciprocating compressor, the methodcomprising the steps of: a) measuring and storing a phase differencebetween a first square wave corresponding to a current supplied to thecompressor and a second square wave corresponding to a stroke of thecompressor by driving the compressor at an initial angle of ignition; b)measuring a phase difference between the first square wave and thesecond square wave by driving the compressor at varied angle ofignition; and c) comparing the measured phase difference with a storedphase difference, to vary the angle of ignition so that the measuredphase difference is smaller than the stored phase difference and tocontrol the compressor at the angle of ignition at which the phasedifference is minimzed.

[0063] In still another aspect of the present invention, there isprovided a method for controlling a position of a piston of areciprocating compressor, the method comprising the steps of: a)generating a first square wave corresponding to a current supplied tothe compressor by the compressor at a certain angle of ignition; b)generating a second square wave corresponding to a stroke of thecompressor; and c) adjusting the angle of ignition according to a phasedifference between the first and second square waves to controloperation of the compressor.

[0064] At the step c, a control signal for controlling the piston isoutputted so that a top clearance is minimized according to the phasedifference between the first and second square waves.

[0065] In still anther aspect of the present invention, there isprovided a method for controlling a reciprocating compressor, the methodcomprising the steps of: a) tabling and storing a phase differencebetween a current corresponding to a load and a stroke; b) measuring apresent load, and reading the phase difference corresponding to themeasured load from the table; c) measuring a phase difference between acurrent supplied to the compressor and a stroke of the compressor bydriving the compressor at an initial angle of ignition; and d) comparingthe measured phase difference with the read phase difference to vary theangle of ignition so that the measured phase difference is close to theread phase difference.

[0066] The step c comprises the steps of detecting the current suppliedto the compressor and generating a first square wave corresponding tothe current, detecting a voltage supplied to the compressor, calculatingthe stroke of the compressor using the detected voltage and current,generating a second square wave corresponding to the calculated stroke,and measuring a phase difference between the first and second squarewaves.

[0067] The first square wave is generated by integrating the detectedcurrent.

[0068] At the step c, the initial angle of ignition is set so that thephase difference between the current supplied to the compressor and thestroke of the compressor is sufficiently larger than the read phasedifference, and at the step d, by controlling the angle of ignition tocause the phase difference between the current supplied to thecompressor and the stroke of the compressor to be gradually decreased,and by comparing the measured phase difference with the read phasedifference, the compressor is controlled at a previous angle of ignitionat a moment that the measured phase difference is smaller than the readphase difference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The above objects, other features and advantages of the presentinvention will become more apparent by describing the preferredembodiment thereof with reference to the accompanying drawings, inwhich:

[0070]FIG. 1 is a cross sectional view illustrating the construction ofa reciprocating compressor disclosed in U.S. Pat. No. 5,342,176.

[0071]FIG. 2 is a block diagram illustrating a compressor controllingapparatus for controlling a piston stroke of the refrigerant shown inFIG. 1.

[0072]FIG. 3 is a block diagram of a conventional control apparatus fora reciprocating compressor disclosed in the Japanese Patent Laid-OpenPublication hei 9-112438.

[0073]FIG. 4 is a block diagram of another conventional controlapparatus for a reciprocating compressor disclosed in the JapanesePatent Laid-Open Publication hei 9-112438.

[0074]FIG. 5 is a block diagram of an apparatus for controlling areciprocating compressor according to a first preferred embodiment ofthe present invention.

[0075]FIG. 6 is a detail diagram of a control section of FIG. 5.

[0076]FIGS. 7a to 7 h are views illustrating waveform output from eachsection of FIG. 5.

[0077]FIGS. 8a and 8 b are views illustrating a phase difference betweena current phase and a stroke phase according to the present invention.

[0078]FIG. 9 is a view illustrating a variation at a certain pressure ofthe current phase and the stroke phase according to the presentinvention.

[0079]FIG. 10 is a flow chart illustrating a method for controlling areciprocating compressor according to an embodiment of the presentinvention.

[0080]FIG. 11 is a flow chart illustrating a method for controlling thereciprocating compressor according to a second preferred embodiment ofthe present invention, in which a stroke is controlled depending uponthe load.

BEST MODE FOR CARRYING OUT THE INVENTION

[0081] Now, preferred embodiments of the present invention will bedescribed in detail with reference to the annexed drawings.

[0082]FIG. 5 is a block diagram of an apparatus for controlling areciprocating compressor according to a first preferred embodiment ofthe present invention, and FIG. 6 is a detail diagram of a controlsection of FIG. 5.

[0083] The control apparatus of the reciprocating compressor accordingto the first embodiment of the present invention comprises, as shown inFIG. 5, a power supply section 100 for supplying a common power(alternate current of 100 to 220 V), a TRIAC 110 for switching thecommon supplied from the power supply section 100 in response to acontrol signal, a current phase detecting section 30 for detecting acurrent supplied to the compressor through the TRIAC 110 to produce afirst square wave corresponding to the detected current, a motor 40 forreciprocating a piston in a cylinder of the compressor according to thecommon power supplied from the TRIAC 110, a stroke phase detectingsection 50 for outputting a second square wave corresponding to theposition according to the linear motion of the piston, a zero crossingdetecting section 60 for detecting a zero crossing of the common powersupplied from the power supply section 100, a control section 70 foroutputting the control signal for controlling the position of the pistonaccording to the phase difference between the first square wave producedfrom the current phase detecting section 30 and the second square waveproduced from the stroke phase detecting section 90, and a phase controlsection 80 for controlling an angle of ignition for controlling thestroke of the compressor according to the control signal outputted fromthe control section 70, and outputting the signal to the TRIAC 110.

[0084] The current phase detecting section 30 includes a currentdetecting section 31 switched through the TRIAC 110 to detect a currentsupplied to the motor 40 of the compressor, an integrating section 32for integrating the current detected from the current detecting section,and a first square wave generating section 33 for generating a firstsquare wave corresponding to the integrated current from the integratingsection 32.

[0085] The stroke phase detecting section 50 includes a voltagedetecting section 53 for detecting a voltage supplied to the motor ofthe compressor, a stroke computing section 51 for computing the strokeaccording to the reciprocating motion of the piston according to thevoltage value detected from the voltage detecting section 53 and thecurrent value detected from the current detecting section 32, and asecond square wave generating section 52 for generating a second squarewave corresponding to the stroke computed from the stroke computingsection 51.

[0086] The control section 70 includes a phase difference measuringsection 71 for measuring a phase difference between the first squarewave outputted from the current phase detecting section 30 and thesecond square wave outputted from the stroke phase detecting section 50,a phase difference storing section 72 for storing the phase differencedetected from the phase difference measuring section 72 according to thecontrol signal, a phase difference comparing section 73 for comparingthe phase difference stored in the phase difference storing section 72with the phase difference measured from the phase difference measuringsection 71, and a determining section 74 for determining a dimension ofthe angle of ignition according to the compared result from the phasedifference comparing section and outputting a stored enable signal ofthe phase difference storing section 72.

[0087] A method for controlling the reciprocating compressor accordingto the present invention will now be described.

[0088]FIGS. 7a to 7 h are views illustrating a waveform outputted fromeach section of FIG. 5, FIGS. 8a and 8 b are views illustrating thephase difference between the current phase and the stroke phaseaccording to the present invention, and FIG. 9 is a view illustrating avariation at a certain pressure of the current phase and the strokephase according to the present invention. FIG. 10 is a flow chartillustrating a method for controlling the reciprocating compressoraccording to the first embodiment of the present invention.

[0089] First of all, it will now describe the controlling method of thecompressor according to the first embodiment of the present invention.

[0090] In case the common current having a constant frequency issupplied to the power supply section 100, as shown in FIG. 7a, the phasecontrol section 80 applies a triggering signal according to a certainangle of ignition to the TRIAC 110 to drive the motor 40 of thecompressor (step 1S).

[0091] The current detecting section 31 and the voltage detectingsection 53 detect the current and voltage of the power supplied to themotor of the compressor, respectively (step 2S). At that time, thecurrent detected from the current detecting section is detected as shownin FIG. 7c, the voltage detected from the voltage detecting section 53is detected as shown in FIG. 7d (counter electromotive force of themotor).

[0092] The first square wave corresponding to the current detected fromthe current phase detecting section 30 is outputted to the controlsection 70 (step 3S).

[0093] Specifically, the integrating section 32 of the current phasedetecting section 30 integrates and outputs the current detected fromthe current detecting section 31, as shown in FIG. 7e, and the firstsquare wave generating section 33 generates the first square wavecorresponding to the integrated value and outputs it to the controlsection 70, as shown in FIG. 7f.

[0094] At that time, the stroke phase detecting section 50 estimates thestroke according to the reciprocating motion of the piston (step 4S),and generates an alternate voltage waveform and generates the secondsquare wave corresponding to the alternate voltage waveform (step 5S),of which a frequency is maintained and an amplitude is varied, dependingupon a location of the reciprocating piston.

[0095] The stroke estimation is carried out by the following equation.$X = {\frac{1}{\alpha}{\int{\left( {{Vm} - {Ri} - {L\frac{i}{t}}} \right){t}}}}$

[0096] wherein, Vm is a voltage supplied to both terminals of the motor,I is a current supplied to the motor, R is a resistance of a motorwinding, and L is an inductance of the motor winding.

[0097] The stroke computing section 51 of the stroke phase detectingsection 50 generates the alternate voltage waveform, of which afrequency is maintained and an amplitude is varied, depending upon alocation of the reciprocating piston, and the second square wavegenerating section 52 generates the second square wave corresponding tothe alternate voltage waveform generated from the stroke computingsection 51, as shown in FIG. 7h.

[0098] Also, the zero crossing detecting section 60 detects a zerocrossing of AC 220 V supplied from the power supply section 100.

[0099] The control section 70 detects the phase difference between thefirst square wave outputted from the current phase detecting section 30and the second square wave outputted from the stroke phase detectingsection 50 using the signal of the zero crossing detecting section 60(step 6S), and compares the detected phase difference with the storedphase difference (steps 7S to 10S) and outputs the signal forcontrolling the location of the piston according to the comparison(steps 11S to 15S).

[0100] Specifically, the phase difference detecting section 71 of thecontrol section 70 detects the phase difference between the first squarewave outputted from the current phase detecting section 30 (as shown inFIG. 5a) and the second square wave outputted from the stroke phasedetecting section 50 (as shown in FIG. 8b)(step 6S). It does not matterto detect an interval (D1) between a downstream edge of the secondsquare wave and a downstream edge of the first square wave, an interval(D2) between a downstream edge of the second square wave and an upstreamedge of the first square wave, an interval (D3) between an upstream edgeof the second square wave and a downstream edge of the first squarewave, or an interval (D4) between an upstream edge of the second squarewave and an upstream edge of the first square wave.

[0101] At that time, since there is no previous phase difference at anearly stage (step 7S), the detected phase difference is stored in thephase difference storing section 72 (step 8S), and the angle of ignitionis varied in a certain direction to drive the compressor (step 9S). Andthen, the processes (steps 2S to 7S) are repeated.

[0102] If the phase difference is newly detected through the repeat ofthe above process (step 7S), the phase difference comparing section 73of the control section 70 compares the present detected phase differencewith the stored phase difference (step 10S), and the determining section74 of the control section 70 outputs a signal for controlling a variabledirection of the angle of ignition according to the comparison results,and simultaneously outputs an enable signal for commanding whether thephase difference storing section 72 stores the present detected phasedifference or not. Accordingly, the phase control section 80 controlsthe angle of ignition of the TRIAC 110 according to the control signaloutputted from the determining section 74 of the control section 70.

[0103] Specifically, if the control section 70 compares the presentdetected phase difference with the stored phase difference (step 10S),and if the present detected phase difference is lower than the storedphase difference (step 11S), the present detected phase difference isnewly stored (step 12S), and the control signal for commanding the angleof ignition to be varied in a previously varied direction is outputtedto the phase difference control section 80 to vary the angle of ignition(step 13S). For example, if the varied angle of ignition is varied in alarge direction, the angle of ignition is more increased, and if thevaried angle of ignition is varied in a small direction, the angle ofignition is more decreased.

[0104] By contrast, if the control section 70 compares the presentdetected phase difference with the stored phase difference (step 10S),and if the present detected phase difference is larger than the storedphase difference (step 11S), the present detected phase difference isnot stored, and the previously stored phase difference is constantlymaintained. The control signal for commanding the angle of ignition tobe varied in a direction opposed to the previously varied direction isoutputted to the phase difference control section 80 to vary the angleof ignition (step 14S). For example, if the varied angle of ignition isvaried in a large direction, the angle of ignition is more decreased,and if the varied angle of ignition is varied in a small direction, theangle of ignition is more increased.

[0105] If the above process is repeated to allow the stored phasedifference and the present detected phase difference to be equal to eachother (steps 11S and 14S), the stroke of the compressor is controlled,thereby providing a maximum efficiency.

[0106]FIG. 9 shows an inflection point in which the phase differencebecomes to be minimized. It is regarded that the inflection point iszero of a top clearance of the piston.

[0107] In the phase control, in case of driving the compressor at asufficiently large value of initial angle of ignition, it is controlledthe angle of ignition is varied in a gradually reduced direction. Incase of becoming the phase difference to be large at a moment, thecompressor is controlled by the angle of ignition controlled at previousstep, In order words, the compressor is controlled by the angle ofignition at the inflection point.

[0108] Accordingly, the TRIAC 110 switches the voltage supplied from thepower supply section 100 according to the angle of ignition outputtedfrom the phase control section 80, and, with repeating the aboveprocess, the control section 70 controls the piston of the compressor,so that the top clearance is minimized.

[0109] A method for controlling the reciprocating compressor accordingto a second preferred embodiment of the present invention will now bedescribed.

[0110]FIG. 11 is a flow chart illustrating a method for controlling thereciprocating compressor according to the second preferred embodiment ofthe present invention, in which a stroke is controlled depending uponthe load.

[0111] The embodiment of the present invention controls the stroke ofthe piston of the compressor depending upon the load, in which if theload is small, the stroke of the piston is controlled to be small, whileif the load is large, the stroke of the piston is controlled to belarge. Accordingly, the top clearance is not minimized, but thecompressor is controlled to have the top clearance corresponding to theload.

[0112] The current phase corresponding to the stroke of the pistondepending upon the load acting onto the compressor and the phasedifference between the stroke are tabled through several experiments andare stored (step 21S).

[0113] A control section 70 measures the load of the refrigerator (step22S). The method for measuring the load of the compressor is well knownin the prior art. The load is measured by detecting a temperature of theinside of the refrigerator, a temperature of the coolant flowing througha heat exchanger, or a temperature of the periphery of the refrigerator.The phase difference (corresponding to the measured load is read fromthe table (step 23S).

[0114] The phase control section 80 applies a triggering signalaccording to a certain angle of ignition to the TRIAC 110 to drive themotor 40 of the compressor (step 24S).

[0115] The current detecting section 31 and the voltage detectingsection 53 detect the current and voltage of the power supplied to themotor of the compressor, respectively (step 25S). The first square wavecorresponding to the current detected from the current phase detectingsection 30 is outputted to the control section 70 (step 26S). At thattime, the stroke phase detecting section 50 estimates the strokeaccording to the reciprocating motion of the piston (step 27S), andgenerates an alternate voltage waveform and generates the second squarewave corresponding to the alternate voltage waveform (step 28S).

[0116] The stroke estimation is carried out by the following equation.$X = {\frac{1}{\alpha}{\int{\left( {{Vm} - {Ri} - {L\frac{i}{t}}} \right){t}}}}$

[0117] wherein, Vm is a voltage supplied to both terminals of the motor,I is a current supplied to the motor, R is a resistance of a motorwinding, and L is an inductance of the motor winding.

[0118] Also, the zero crossing detecting section 60 detects a zerocrossing of AC 220 V supplied from the power supply section 100.

[0119] The control section 70 detects the phase difference β of thefirst square wave outputted from the current phase detecting section 30and the second square wave outputted from the stroke phase detectingsection 50 using the signal of the zero crossing detecting section 60(step 29S), and compares the detected phase difference β with the phasedifference a corresponding to the present load read from the table (step30S).

[0120] If the read phase difference cc is smaller than the measuredphase difference β (step 31S), the angle of ignition of the TRIC 110 isvaried in such a way that the phase difference between the current phasedetected from the current phase detecting section 30 and the strokephase detected from the stroke phase detecting section 50 becomes to besmall (step 32S). If the read phase difference ox is larger than themeasured phase difference β (step 31S), the angle of ignition of theTRIAC 110 is varied in such a way that the phase difference between thecurrent phase detected from the current phase detecting section 30 andthe stroke phase detected from the stroke phase detecting section 50becomes to be large (step 33S). At that time, the method for varying theangle of ignition is similar to that of the first embodiment of thepresent invention.

[0121] If the above process is repeated to similar the phase differencecorresponding to the load to the detected phase difference (steps 25S to33S), it is possible to control the compressor to be operated at astroke suitable for the load.

[0122] The following effects are provided with the apparatus and methodfor controlling the reciprocating compressor according to the presentinvention.

[0123] The location of the piston in the cylinder is controlled so thatthe top clearance is minimized based on the information of the phasedifference between the current square wave produced by the phase controland the square wave produced by the stroke. Therefore, since thecomplicated operation is not needed, the reciprocating compressor may becontrolled to have a maximum efficiency using an inexpensive cost.

[0124] Since the compressor is controlled by the stroke corresponding tothe load, it is unnecessary to drive the compressor during a desiredtime and to stop the compressor during a desired time, thereby extendinga lifetime of the compressor and minimizing the noise of the compressor.

[0125] At that time, since there is no previous phase difference at anearly stage (step 7S), the detected phase difference is stored in thephase difference storing section 72 (step 8S), and the angle of ignitionis varied in a certain direction to drive the compressor (step 9S). Andthen, the processes (steps 2S to 7S) are repeated.

[0126] If the phase difference is newly detected through the repeat ofthe above process (step 7S), the phase difference comparing section 73of the control section 70 compares the present detected phase differencewith the stored phase difference (step 10S), and the determining section74 of the control section 70 outputs a signal for controlling a variabledirection of the angle of ignition according to the comparison results,and simultaneously outputs an enable signal for commanding whether thephase difference storing section 72 stores the present detected phasedifference or not. Accordingly, the phase control section 80 controlsthe angle of ignition of the TRIAC 110 according to the control signaloutputted from the determining section 74 of the control section 70.

[0127] Specifically, if the control section 70 compares the presentdetected phase difference with the stored phase difference (step 10S),and if the present detected phase difference is lower than the storedphase difference (step 11S), the present detected phase difference isnewly stored (step 125), and the control signal for commanding the angleof ignition to be varied in a previously varied direction is outputtedto the phase difference control section 80 to vary the angle of ignition(step 13S). For example, if the varied angle of ignition is varied in alarge direction, the angle of ignition is more increased, and if thevaried angle of ignition is varied in a small direction, the angle ofignition is more decreased.

[0128] By contrast, if the control section 70 compares the presentdetected phase difference with the stored phase difference (step 10S),and if the present detected phase difference is larger than the storedphase difference (step 11S), the present detected phase difference isnot stored, and the previously stored phase difference is constantlymaintained. The control signal for commanding the angle of ignition tobe varied in a direction opposed to the previously varied direction isoutputted to the phase difference control section 80 to vary the angleof ignition (step 14S). For example, if the varied angle of ignition isvaried in a large direction, the angle of ignition is more decreased,and if the varied angle of ignition is varied in a small direction, theangle of ignition is more increased.

[0129] If the above process is repeated to allow the stored phasedifference and the present detected phase difference to be equal to eachother (steps 11S and 14S), the stroke of the compressor is controlled,thereby providing a maximum efficiency.

[0130] Industrial Applicability

[0131] As apparent from the above description, according to the presentinvention, since the position of the piston in the cylinder iscontrolled so that the top clearance is minimized according to theinformation of phase difference between the square wave of the currentand the square wave of the stroke, there is no needed a complicatedcalculation, thereby inexpensively and efficiently controlling thereciprocating compressor and improving the reliability thereof.

[0132] Since the compressor is controlled by the stroke corresponding tothe load, it is unnecessary to drive and stop the compressor during aconstant period, thereby extending a lifetime of the compressor andminimizing the noise the compressor.

We claims:
 1. An apparatus for controlling a reciprocating compressor,the apparatus comprising: a driving section for driving thereciprocating compressor by varying an angle of ignition in response toa control signal; a current phase detecting section for outputting asquare wave corresponding to the detected current supplied to thecompressor; a stroke phase detecting section for outputting a squarewave corresponding to a stroke of the compressor; and a control sectionfor controlling the angle of ignition of the driving section accordingto the phase difference between the square wave produced from thecurrent phase detecting section and the square wave produced from thestroke phase detecting section.
 2. The apparatus as claimed in claim 1,wherein the current phase detecting section includes a current detectingsection for detecting the current supplied to the compressor to output adetected current value, and a first square wave generating section foroutputting a first square wave corresponding to the current detectedfrom the current detecting section.
 3. The apparatus as claimed in claim2, wherein the current phase detecting section further includes anintegrating section for integrating the current detected from thecurrent detecting section to output the integrated current to the firstsquare wave generating section.
 4. The apparatus as claimed in claim 1,wherein the stroke phase detecting section includes a voltage detectingsection for detecting a voltage supplied to the compressor, a strokecomputing section for computing the stroke based on the voltage detectedfrom the voltage detecting section and the current detected from thecurrent detecting section, and a second square wave generating sectionfor generating a second square wave corresponding to the stroke computedfrom the stroke computing section to output the second square wave tothe control section.
 5. The apparatus as claimed in claim 1, wherein thecontrol section includes a phase difference measuring section formeasuring a phase difference between a current waveform outputted fromthe current phase detecting section and a stroke waveform outputted fromthe stroke phase detecting section, and an output voltage commandingsection for determining a target output voltage according to a size ofthe phase difference measured from the phase difference measuringsection.
 6. The apparatus as claimed in claim 5, wherein the outputvoltage commanding section includes a phase difference storing sectionfor storing the phase difference detected from the phase differencemeasuring section, a phase difference comparing section for comparingthe phase difference stored in the phase difference storing section withthe phase difference measured from the phase difference measuringsection, and a determining section for determining the voltage to besupplied to the compressor according to the compared result from thephase difference comparing section and outputting a write enable signalof the phase difference storing section.
 7. The apparatus as claimed inclaim 1, wherein the determining section determines whether a top ofclearance is zero when the phase difference is minimized.
 8. Theapparatus as claimed in claim 6, wherein the determining section outputsa write enable signal so that when the phase difference detected fromthe phase difference measuring section is lower than that stored in thephase difference storing section, the phase difference storing sectionstores the phase difference detected from the phase difference measuringsection.
 9. The apparatus as claimed in claim 1, wherein the drivingsection includes a TRIAC for supplying the power to the compressor inresponse to a control signal, and a phase control section forcontrolling an angle of ignition for controlling the stroke of thecompressor according to a control signal outputted from the controlsection and outputting the signal to the TRIAC.
 10. The apparatus asclaimed in claim 9, wherein the TRIAC switches the power according tothe angle of ignition outputted from the phase control section.
 11. Theapparatus as claimed in claim 1, further comprising a zero crossingdetecting section for detecting a zero crossing of a voltage of thepower supplied from the driving section.
 12. A method for controlling areciprocating compressor, the method comprising the steps of: a) drivingthe compressor by varying an angle of ignition, and measuring a phasedifference between a current phase supplied to the compressor and astroke phase of the compressor when the angle of ignition is varied; andb) comparing the measured phase differences, and driving the compressorat the angle of ignition corresponding to an inflection point of thephase difference.
 13. The method as claimed in claim 12, wherein thephase difference is minimized at the inflection point.
 14. The method asclaimed in claim 12, wherein the current phase is generated by detectingthe current supplied to the compressor and integrating the detectedcurrent.
 15. The method as claimed in claim 12, wherein the stroke phaseis outputted as a pulse corresponding to an estimated value afterdetecting the voltage and the current supplied to the compressor andestimating the stroke using the detected voltage and current.
 16. Themethod as claimed in claim 12, wherein the step a comprises the steps ofstoring the detected phase difference when driving the compressor at aninitial angle of ignition; measuring the phase difference by varying theangle of ignition in a desired direction; comparing the measured phasedifference with a previously stored phase difference; substituting themeasured phase difference for the stored phase difference if themeasured phase difference is smaller than the stored phase difference;and repeating the measuring, comparing and substituting steps by varyingthe angle of ignition in same direction.
 17. The method as claimed inclaim 16, further comprising the step of varying the angle of ignitionin a direction opposed to the previously varied direction, if themeasured phase difference is larger than the initially stored phasedifference.
 18. The method as claimed in claim 16, wherein thecompressor is controlled by recognizing the angle of ignition as aninflection point of a previous step, if the measured phase difference islarger than the previously stored phase difference.
 19. The method asclaimed in claim 12, wherein at the step a, the phase difference ismeasured by setting the angle of ignition to supply the current ofsufficiently small value to the compressor at early stage and by varyingthe angle of ignition to supply the current of gradually increasingvalue to the compressor, and at the step b, the compressor is controlledby recognizing the angle of ignition as the inflection point of aprevious step, when the measured phase difference is larger than thepreviously stored phase difference.
 20. A method for controlling areciprocating compressor, the method comprising the steps of: a)measuring and storing a phase difference between a first square wavecorresponding to a current supplied to the compressor and a secondsquare wave corresponding to an estimated stroke of the compressor, bydriving the compressor at a desired angle of ignition; b) measuring aphase difference between a first square wave corresponding to thecurrent supplied to the compressor and a second square wavecorresponding to an estimated stroke of the compressor, by driving thecompressor at varied angle of ignition in a desired direction; c)comparing the measured phase difference with a stored phase difference,to vary the angle of ignition in an opposed direction, if the measuredphase difference is larger than the stored phase difference, and tosubstitute the measured phase difference for the stored phase differenceand vary the angle of ignition in same direction, if the measured phasedifference is smaller than the stored phase difference; and d) repeatingthe steps b and c to drive the compressor at a point in which the phasedifference is deflected.
 21. A method for controlling a reciprocatingcompressor, the method comprising the steps of: a) measuring and storinga phase difference between a first square wave corresponding to acurrent supplied to the compressor and a second square wavecorresponding to a stroke of the compressor by driving the compressor atan initial angle of ignition; b) measuring a phase difference betweenthe first square wave and the second square wave by driving thecompressor at varied angle of ignition; and c) comparing the measuredphase difference with a stored phase difference, to vary the angle ofignition so that the measured phase difference is smaller than thestored phase difference and to control the compressor at the angle ofignition at which the phase difference is minimized.
 22. A method forcontrolling a position of a piston of a reciprocating compressor, themethod comprising the steps of: a) generating a first square wavecorresponding to a current supplied to the compressor by the compressorat a certain angle of ignition; b) generating a second square wavecorresponding to a stroke of the compressor; and c) adjusting the angleof ignition according to a phase difference between the first and secondsquare waves to control operation of the compressor.
 23. The method asclaimed in claim 22, wherein at the step c, a control signal forcontrolling the piston is outputted so that a top clearance is minimizedaccording to the phase difference between the first and second squarewaves.
 24. A method for controlling a reciprocating compressor, themethod comprising the steps of: a) tabling and storing a phasedifference between a current corresponding to a load and a stroke b)measuring a present load, and reading the phase difference correspondingto the measured load from the table; c) measuring a phase differencebetween a current supplied to the compressor and a stroke of thecompressor by driving the compressor at an initial angle of ignition;and d) comparing the measured phase difference with the read phasedifference to vary the angle of ignition so that the measured phasedifference is close to the read phase difference.
 25. The method asclaimed in claim 24, wherein the step c comprises the steps of detectingthe current supplied to the compressor and generating a first squarewave corresponding to the current, detecting a voltage supplied to thecompressor, calculating the stroke of the compressor using the detectedvoltage and current, generating a second square wave corresponding tothe calculated stroke, and measuring a phase difference between thefirst and second square waves.
 26. The method as claimed in claim 25,wherein the first square wave is generated by integrating the detectedcurrent.
 27. The method as claimed in claim 24, wherein at the step c,the initial angle of ignition is set so that the phase differencebetween the current supplied to the compressor and the stroke of thecompressor is sufficiently larger than the read phase difference, and atthe step d, by controlling the angle of ignition to cause the phasedifference between the current supplied to the compressor and the strokeof the compressor to be gradually decreased, and by comparing themeasured phase difference with the read phase difference, the compressoris controlled at a previous angle of ignition at a moment that themeasured phase difference is smaller than the read phase difference.